;(function(doc, win) {
    var docEl = doc.documentElement,
      isIOS = navigator.userAgent.match(/\(i[^;]+;( U;)? CPU.+Mac OS X/),
      dpr = isIOS ? Math.min(win.devicePixelRatio, 3) : 1,
      dpr = window.top === window.self ? dpr : 1, //被iframe引用时，禁止缩放
      dpr = 1,
      scale = 1 / dpr,
      resizeEvt =
        'orientationchange' in window ? 'orientationchange' : 'resize'
    docEl.dataset.dpr = dpr
    var metaEl = doc.createElement('meta')
    metaEl.name = 'viewport'
    metaEl.content =
      'initial-scale=' +
      scale +
      ',maximum-scale=' +
      scale +
      ', minimum-scale=' +
      scale
    docEl.firstElementChild.appendChild(metaEl)
    var recalc = function() {
      var width = docEl.clientWidth
      if (width / dpr > 1920) {
        width = 1920 * dpr
      }
      // 乘以100，px : rem = 100 : 1
      docEl.style.fontSize = 16 * (width / 1920) + 'px'
    }
    recalc()
    if (!doc.addEventListener) return
    win.addEventListener(resizeEvt, recalc, false)
  })(document, window)